Method of producing lead arsenate



' Patented July as, 1944 assists John Eaglemrrnon or'rnonucma LEAD Assam-rs anemia-Joplin, ma, usignor to The Picher Lead company a corporation of one No Drawing.

This invention relates to insecticides and the method of manufacturing the same whereby I;

am enabled to produce an insecticide such as lead arsenate with a high degree of adhesiveness.

which will permit its retention on foliage for a much longer period of time than known lead arsenates which settles from suspension very slowly; which is practically impervious to the action of water, and which can be so treated as to produce a fast color.

In the preparation of the present lead arsenate of commerce a slurry of litharge' and water is prepared, to which is added arsenic acid in defle nite proportions over a period of time. The resulting precipitate is normally the color of flour, and to guard against its use as food, a red or colored powdered pigment is mechanically blended with the lead arsenate, which serves to identify it as a definite product. In this form a certain amount of lead arsenate is rendered soluble in water by reactionwith the coloring matter, causing loss of product and deleterious eflect on vegetation, from the presence of soluble arsenate. The desirability of a lead ar's'enate with an insoluble fast color has long been recognized, and many unsuccessful attempts have heretofore been made to accomplish this.

In the practice of my invention I have found that the addition of lead silicate to the litharge 'ln definitely regulated quantities enables me to produce a lead arsenate with a high degree of adhesiveness. WhileI have used lead silicate that is basic in nature, I have found the best results can be reached by .using anhydrous basic lead silicate corresponding to any ofthe following compositions: mosioi Tetralead silicate 2PbO.SiOz -Lead orthosilicate PbQSiO2 ..Lead metasilicate Cincinnati, hio,-'

muse... Mayl, 1941, Serial No. sszsas s Claim. (01. 23-54) v I responding hydrated form may be used. In this case the range of composition best suited lies between the lead orthosllicate (2PbO.SiO2) and lead metasilicate' (P'bOSlOz). The hydrated eutectic mixture lead orthosilica'te-lead metasilicate represents the most desirable composition.

Since we have found the substitution of lead silicate for litharge as defined in the application 18 based on the weight percentage of silica in the lead silicate used, the percentage of substitution may vary with the silica content of the lead silicate.

As one example ofthe process used by me in the practice of my invention in which 1% of the lltharge is replaced by its PbO equivalent of lead silicate, I first heat 1429 gallons of water to approximately 90 C., and add, with constant stirring, 3819 pounds or finely divided litharge, mixed with approximately 47 pounds of basic lead silicate, and the whole is stirred rapidly for approxor their eutectics, or mixtures, of these silicates with their eutectics. We have found the best resuits are obtained by using the eutectic mixture lead prthosilicate-lead metasillcate. All these silicates decompose completely on reaction with arsenic acid solution forming lead arsenate and gelatinous silica. Furthermore, all the silica librange from 6.3% to 21.2% of silica. However, a lead silicate whose composition represents a mixj ture of tetra lead silicate (4PbO.SlO:) and PbO is equally eilective.

Instead of the anhydrous lead silicate, the corimately 15 minutes. Cold water is next added in asufllcient quantity to dilute the mixture to approximately 2800 gallons, and lower the temperatureto C. Arsenic acid equivalent toapproximately 1989 pounds of A5205 with a proportlon of 61% A5205 is then added in the proportion of approximately V; in the first 1 hours,

,i'or instance, substituted 1% or lead silicate for the PhD equivalent of litharge.

Again I have substituted an equivalent amount of hydrated lead silicate for the entire PbO content. In normal practice I have found good results are reached by using a replacement of from .5% to 5% of the litharge with its PbO equivalent oi lead silicate when the lead silicate has a PhD content of 83.5% and SiO: 14.7%; the balance being combined water; Within the limits of 1% to 2% the amount of lead silicate added may be regarded as critical. The beneficial results obtained are due in part to the silica gel formed. during precipitation, and which is considered to be present as a surface coating on'the lead arsenate particles. I have, for example, produced highly beneficial eiIects when the silica gel is present on the particles in an amount varying from 0.1% to 1%, although other proportions tor-shipment. x

haveprovedbeneflcial. Inthosecases whenit isdesiredtorendertheleadarsenate more water repellent and permanent in nature. I have found the addition 01' an oil soluble and water insoluble dye serves to coat the pigment particle without meeting-its adhesiveness or impairing its properties as an insecticide. In order to distribute the and utilize the dye completely it is necesary to add the oil solution in the form of an in water and thus make the microscopic oil globules more readily available. to the particles of insecticide throughout the slurry. Again. I may dissolve the emulsifying alent in the solvent together with the dye and add the solution to the slurry of arsenate and silica and in this manner emulsify the dye solution in the slurry. The precipitated, colored lead arlenate is then filter pressed and dried'at a temperature of 100 0., pulverized and .packed Ky coloring process is to he distinguished from thosecases ofcolorlng lead arsenate and other matcrialsinwhichthecolorisaddedasadry powder that dilutes the lead arsenate and decreases the Y concentration and effectiveness Purther, my coloring process must not becmfuseilwiththoseinwhich the dyeisadded as a water solution. The liquor is colored and much of the dye is lost in the process, and the absorbed dye tends-to bleed during use. My proceq eliminates casehardening and all the dye is utilized so that a smaller quantity is effective as compared with a larger quantity required in. a solution. In the prepared form lead arsenate made by my process has the formula 2PbOAssOaHzO or PbliAsOl with the admixture 'of approximately 0.15 :per cent of gelatinous By my process I am enabled to achieve the new and imobvious results of improved suspension of the insecticide in water slurry, and of improved adhesionoftheleadarsenatesopreparedtofruit foliage. The improvement in suspension due tothepresenoeoi'silicagelinleadarsenate'isbythe following table. The numerical represent the apparent volume in cimic o c pied by'15 grams of the insecti-I cide at one minute intervals aiterdispersion m? acid. basic or normal and should be free from uncombined lead oxide or silica and physically and chemically homogeneous.

Having thus described my invention, what 1 20 claim as new'and desire to secure by Letters Patent is: I v

'1. The method for producing lead arsenate, which comprises adding arsenic acid to lead silicate and decomposing thelead silicate to form lead arsenate in the presence of precipitated silica, said precipitated silica being coated on'ths particles of lead arsenate.

2. The method for producing lead arsenate which comprises adding arsenic acid to a mixture of litharge and lead silicate and decomposing the lead silicate to'iorm lead arseniate in the presence of precipitated silica and coating the particles. of lead arsenate withthe precipitated 3. The method for producing lead arsenate which comprises adding arsenic acid toa of litharge and lead silicate, iorming a slurry .fi'om-the mixture and precipitating lead arsenate I coated with precipitated silica mm the slurry.

- 4. The process for producing lead arsenate which comprises mixing b s lead silicate and arsenic acid and forming ja slurry therefrom and precipitating from theslurry lead arsenate in the presence of precipitated silica.

5-. The process for producing lead arsenate which comprises mi'xing'basiclead silicate, lithuse and a nic acid arid-remiss a slur y thereso nate insiie Q! from and precipitating'irom lead arseprecipitated silica. we? o L 

